Electric discharge device



Nov. 6, 1934. W.YTRAUB 1,980,017

ELECTRIC DISCHARGE DEVICE Filed Oct. 20. 1931 Fig. 3.

Inventor: Wilheh fi Tw-aub,

' His Atfiorneg.

Patented Nov. 6, 1934 x ELECTRIC DISCHARGE DEVICE Wilhelm Traub, Charlott enburg, Germany, assignor to General Electric Company, a corporation of New York Application October 20, 1931, Serial No. 570,005

. In Germany October 28, 1930 Claims. (01. 250-45) The present invention relates to electric discharge devices and more particularly to high vacuum X-ray tubes.

In the case of high vacuum discharge devices,

5 especially tubes for high voltage, such as X-ray tubes, it is customary to protect the walls of the tube against puncture by means of metal cylinders positioned at appropriate places. In the prior art, there are X-ray tubes in which a portion of the envelope surrounding the discharge zone consists of metal in order to preventthe said puncturing effect. There are also tubes in which the envelope is constituted entirely of glass and the discharge zone is surrounded by a pair of metal cylinders, one interior and the other exterior of the envelope, concentrically arranged, and in electrical connection with one another. Tubes of this general character offer some advantage by-way of avoiding puncture but they have the disadvantage of allowing theenvelope, also the metal cylinders, to acquire a high negative potential.

It has been proposed in order to reduce this potential and thereby to improve the operation of the tube, that the metal portion of the envelope or the cylinders be insulated from the cathode. Notwithstanding the improvement in operation thus obtained, it is still found that the metal portions acquire a potential too high to allow ready handling of the tube. In accordance with the present invention, this disadvantage is substantially avoided so that it is now possible to use the metal members referred to, without permitting the high potential charge to alfect the handling and operation of the tube.

The invention briefly stated consists in providing an X-ray tube of the kind described with a vacuum chamber or enclosure surrounding the outer metal member. This vacuum chamber may be separated completely from the tube discharge space but preferably, is connected with such space at suitable places by openings of restricted dimension.

The vacuum chamber may be constituted, partly or entirely, of any suitable material, for example metal or insulating material. In the case of a metal enclosure, it is desirable to have the metal of such shape and thickness that it may yield readily to longitudinal pressure in order to prevent rupture at the fusion points of the chambet with the discharge tube. When the chamber is fabricated entirely or partly of an insulating material such as glass, the latter preferably should be of such thickness that the casing cannot be punctured by the high voltages employed during operation. The enclosure may also be composed partly of insulating material and partly of metal, in Which'case the metal portion preferably is of flexible character so as to prevent rupture due to thermal expansion.

The invention will be better understood when reference is made to the following specification and the accompanying drawing in which Fig. 1 represents an exemplary embodiment of my invention, while Figs. 2 and 3 illustrate modifi cations.

Referring to Fig. l, numeral 1 designates the envelope of an X-ray tube which terminates in oppositely directed reentrant stems 2. The envelope contains an anode 3 and a cathode 4 of any suitable construction secured in any appropriate manner to the reentrant stems. There are provided about the active region of the discharge, a pair of metal cylinders 5 which advantageously maybemade of tungsten, tantalum or the like, in order to absorb X-rays generated radially of the tube. These tubes may or may not fit snugly about the envelope and are maintained at the same potential by means of a conductor 6 passing through the glass wall. The cathode 4 may be enclosed in a metal cylinder in order to prevent the escape of X-rays or cathode rays. The purpose of the cylinders 5 is to prevent puncture of the glass in the region of the discharge. While it has beenfound that these cylinders effectively serve this purpose under the conditions stated, they also acquire a high potential which precludes ready handling of the tube.

In accordance with the present invention, an additional enclosure or casing '7, preferably of cylindrical form, is provided about the outer metal cylinder and fused at each end to the glass envelope. There is a small opening 8 at the places where the enclosure joins the glass so as to bring the interior of the enclosure into communication with the interior of the envelope for evacuation purposes. These openings are too small to permit a discharge to pass into the outer chamber.

It is apparent that in the device shown in Fig. 1, the wall of the envelope at the discharge zone is ensured against puncture by means of the inner and outer cylinders 5 maintained at the same potential and that the high potential normally acquired by these cylinders constitutes little or no disadvantage on account of the surrounding shield '71. The vacuum space within the latter introduces sufiicient insulation to prevent any points of high potential on the exterior surface of the tube. It is therefore possible to bring earth objects nearer to the tube Without destroying the focus than was possible heretofore and furthermore, the mounting and operation of the tube are greatly improved. It is even possible to enclose the tube directly in an earthed metal container.

In Fig. 2, the evacuated chamber 7 is constituted partly of glass where it joins the envelope and partly of metal. The latter preferably is positioned symmetrical with respect to the cylinders 5 and is made of sylphon or other flexible material so as to allow for longitudinal expansion under operating conditions. As in the case of Fig. 1, the chamber is provided with a small aperture at each end in order to facilitate evacuation of the enclosure and if desired, the cathode may be provided with a metal hood to prevent radial emanation of X-rays or cathode rays.

In Fig. 3, the casing 7 is constituted entirely of glass as in the case of Fig. 1 but the inner wall 9 of the casing is fused to the main envelope only at one end. The other end of the wall terminates short of the, envelope and in a flared portion so as to leave a small annular space through which the chamber may be evacuated. This wall member supports the two metal cylinders 5 joined together by the conductor 6.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An X-ray tube comprising an evacuated envelope containing an anode and a cathode, a plurality of metal cylinders surrounding the discharge region between said electrodes, one of said cylinders being mounted on the interior of the envelope and another of said cylinders being mounted on the exterior of the envelope, said cylinders being maintained at the same potential, an evacuated enclosure surrounding a por tion of the envelope about said cylinders, said enclosure containing the exterior cylinder and being in communication with the interior of said envelope.

2. An electron discharge device comprising an evacuated glass envelope containing an anode and a cathode, a metal cylinder surrounding the discharge region between said anode and cathode, an evacuated enclosure surrounding a portion of the envelope about said cylinder, said enclosure consisting of glass portions joined to an intermediate metal portion.

3. An electron discharge device comprising an evacuated glass envelope containing an anode and a cathode, a metal cylinder surrounding the discharge region between said anode and cathode, an evacuated enclosure surrounding a portion of the envelope about said cylinder, said enclosure consisting of glass portions joined to an intermediate metal portion, said metal portion being constituted of flexible material.

4. An X-ray tube comprising an evacuated glass envelope containing an anode and a cathode, means for preventing puncture of the envelope during operation and due to high voltage, said means comprising metal cylinders surrounding the discharge region between the anode and cathode, at least one of said cylinders being exterior to the envelope and being subject to the acquisition of a high potential and means for shielding said exterior cylinder, said last mentioned means comprising an evacuated enclosure containing said exterior cylinder.

5. An X-ray tube comprising an evacuated envelope containing an anode and a cathode, a plurality of metal cylinders surrounding the discharge region between said electrodes, one of said cylinders being mounted on the interior of the envelope and another of said cylinders being mounted on the exterior of the envelope, an equipotential conductor connecting said cylinders through the envelope, and an evacuated enclosure surrounding a portion of the envelope about said cylinders, said enclosure containing the exterior cylinder and being in communication with the interior of said envelope.

WILHELM TRAUB. 

